In greenhouses, crop like tomatoes, cucumber, pepper, or more in general plants, are cultivated for an optimal yield. It is a general desire that crop grows as fast as possible in order to be able to harvest as early as possible and to obtain a commercial value as high as possible. Apart from nutrients, the most important growth factors are water, air (with a substantial percentage of carbon dioxide), temperature, and light, and a commercial plant grower will try to control these factors to some optimum values.